Most law students think of proximate cause as the Heartbreak Hill of the Torts marathon, the toughest problem in a course replete with tough intellectual issues. However, the real action today is in the cause-in-fact arena, where tort law is constantly butting heads against an intractable problem: the limits of human knowledge about cause and effect. There is a world of difference between a defendant causing injury to a plaintiff, on the one hand, and the plaintiff proving that she did, on the other. This chapter, for those of you courageous enough to press on, addresses a number of cutting-edge factual causation issues often encountered in the Torts course-and increasingly, in the practice of tort law.
The first complex causation problem is illustrated by the DES cases. DES is a drug that was widely prescribed for several decades to prevent miscarriage, but which has subsequently been shown to cause various medical problems in the daughters of women who took it during pregnancy. Because DES was marketed in chemically identical form by over 200 companies, a plaintiff injured by DES exposure faces a very difficult cause-in-fact problem: Even if all companies were negligent for marketing the drug, only one of them-the manufacturer that manufactured the DES pills her mother took-caused her injuries.
This is an enormously difficult proof problem, but there is nothing conceptually hard about it. Evidently, the health problems DES daughters experience are clearly traceable to DES exposure, so there is no difficulty in determining what caused their injuries. The problem is determining who caused it, since so many drug manufacturers sold DES for use during pregnancy. If we could summon Solomon, our omniscient time traveler, he could solve this problem easily enough, by going back to watch the relevant events and jotting down the name of the manufacturer on the bottle.
Sometimes the plaintiff can solve it, too. She may be able to identify the manufacturer if her mother recalls the shape, color, or brand of DES she took. In many cases, however, the evidence will show that the mother took DES, but not which manufacturer’s pill it was. In such cases, the plaintiff will be unable to establish that a particular manufacturer caused her injury. If she is held to the usual burden to prove causation, she must lose.